The actor Billie Piper this week confirmed rumours that work was under way on a film spin-off for the TV series in which she stars as a high-earning prostitute juggling a complicated private and professional life. "I'm not sure it has legs past four seasons so we're trying to develop a movie," she told the Sun.

The show's fourth series is currently in production for ITV2, and previous seasons have been a surprise hit in the US, where it was broadcast on the Showtime network. To date, the show has been screened in 27 territories, including Slovenia and the Middle East.

The show's stylistic similarities to Sex and the City, whose spin-off film sequel is currently enjoying its second week at the top of the UK charts, have been noted, with Nancy Franklin in The New Yorker pointing out the place of the double-entendre-stuffed voiceover.

Secret Diary of a Call Girl was based on the blog and subsequent books by the pseudonymous Belle de Jour, who wrote about life as a London call girl. They were revealed last year to be written by a research scientist called Brooke Magnanti.